Dear Editor,Oxygen,the terminal electron acceptor for mitochondrial electron transport,is vital for plants because of its role in the production of ATP by oxidative phosphorylation.While photosynthetic oxygen production contributes to the oxygen supply in leaves,reducing the risk of oxygen limitation of mitochondrial metabolism under most conditions,root tissues often suffer oxygen deprivation during normal development due to the lack of an endogenous supply and isolation from atmospheric oxygen.Since changes in oxygen concentration have multiple effects on metabolism and energy production (Geigenberger,2003),tight control of oxygen consumption and homeostasis is likely to be particularly important in underground tissues such as roots.